HP-97 printing problem

I've got an HP-97 which only works partly. I can calculate, but whenever I press any key that causes a printing action, the calc turns off :-( Any idea what's wrong with the calc?

Thanks, Juergen


Is it possible that the battery is low. Or the printer mechanism is jam



based on Chan Tran's precise advice, you can simply press the ADV button, the one at the right side of the printer, and see if the paper advances. If the paper goes without trouble, than both batteries and mechanics are fine; otherwise, Chan Tran's advices are correct and it's most likely to be.

If the problem happens only when a printing command is attempted, than you may have electronics problems.

Let us know about what you get.


Luiz C. Vieira - Brazil


Another possiblity is a shorted transsitor in the H-bridge driver circuit for the printer motor. When the other transistor in that side of the bridge is turned on (to run the motor for either the printing command or the ADV button), then the circuit effectively shorts out the power line.
Needless to say if this is the problem, then the ADV button won't work either. I have seen this once, not in a 97, but in another Topcat that I repaired for somebody. A rather rarer machine than the 97, too...


The battery should be OK. It's a rebuilt one, and I've charged it over night.

The printer mechanism looks fine.

The ADV button does not work. If I press it, the calc turns off.

So it looks like it may be the problem Tony described. I don't know much about electronics. Anyway, is there a chance to fix this?

Thanks, Juergen


Is the print head located in the far right position? It may be that the reed switch (activated by position of print head) is not properly set. I can't remember if this would cause the problem you are seeing.


If the HP97 printhead cannot be made to return to its "home" position the machine will lock up in a loop looking for the "HOME" signal. HOME is generated by a small magnetic reed relay.

There are two main causes of the problem. First is a jammed print head. The other is a bad printer gear. The gear was made of a soft plastic that likes to loose its teeth. See Katie's piece in the Articles section for a possible source of a replacement gear.


Hello, David;

I found very, very interesting this fact. If the HOME sensor is not triggered, than the display blanks and stays like this? Say, you you have the mottor wires simply removed when the head is not at HOME position, than you'll have the same symptom?

Just wondering about it. If so, maybe it's gona be easier to repair if this is the situation

Juergen, have you noticed where is the head parked? Left- or right-most position?

Let us know.


Luiz C. Vieira - Brazil


Yes, the machine will lock up in one of several different ways. It can give a blank display or an "Error" display. It may also light up but go away the first time you hit a key.

If the head is not a HOME when you power it on, the machine tries to move the head to HOME. If it is jammed, HOME never happens, the machine gets hung up.


This really seems to be a problem. I made the following test:

1. I manually moved the print head to its home position by turning the gear with my fingertips.

2. I turned on the calc, entered any number and pressed 'print'. The number gets printed, but then the print head stops and does not move back to its home position.

3. Same test with ADV button. The print head stops in the middle.

I closely looked a the printer mechanics. Did not see any problem.

Any idea why the print head does not move to its home position is highly appreciated.

Thanks, Juergen


Sounds like the paper feed cam and lead screw needs to be cleaned and lubricated. Also the lead screw bushings.

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